The oxygen radical species responsible for the inactivation of phages by ascorbic acid was investigated, using four phages of different nucleic acid types.A scavenger for the superoxide anion radical (O^) and scavengers for the hydroxyl radical (OHà")markedly prevented the inactivation of phages by ascorbic acid.Quenchers for singlet oxygen (1O2) slightly prevented the inactivation.Catalase fully prevented the inactivation, whereas superoxide dismutase only partially prevented it.Phages were markedly inactivated in an OHà"generating system, but not in.anO^-generating system or an 1O2-generating system.These results, taken together, indicate that OH-is the major reactive species and that it is directly responsible for the inactivation of phages by ascorbic acid.